1. Field of the Invention
The present invention relates to a powder forging method for producing aluminum (Al) alloy powder of high proof stress and toughness that can be used for components such as engine components of cars in which toughness is required. More particularly, the present invention relates to a powder forging method for producing an aluminum alloy superior in dynamic strength.
2. Description of the Background Art
A method of powder forging by subjecting an amorphous phase to a heat treatment is disclosed in Japanese Patent Application No. 4-77650 (filed Mar. 31, 1992) (Japanese Patent Laying-Open No. 5-279767) by the inventors of the present application.
A method of heating atomized powder of Al-Fe-Y type to obtain aluminum in a nano structure (a structure of grains or precipitates in nm units) is disclosed in Japanese Patent Laying-Open No. 2-274834.
Atomized powder of Al-Fe-Si-X type (where X is at least one of Ti, Co, Ni, Mn, and Cr) is disclosed in Japanese Patent Application No. 4-113712 (filed May 6, 1992) and corresponding U.S. Pat. No. 5,312,494 by the inventors of the present application.
The above-mentioned Japanese Patent Laying-Open No. 5-279767 and corresponding Application 4-77650 proposing a powder forging method only describes the forging temperature to be "at least the glass transition temperature" (approximately 250.degree.-300.degree. C. in general). The highest temperature described in the embodiment thereof is 550.degree. C. The inventors of the present application carried out various experiments according to that description, and determined that a heating process up to the temperature of 550.degree. C. can be used to achieve favorable values for static strength by a tensile test or the like, but not for dynamic strength represented by Charpy impact values for example.
The alloy disclosed in the above-mentioned Japanese Patent Laying-Open No. 2-274834 and Japanese Patent Application No. 4-113712 is noteworthy of having superior static strength and dynamic strength. However, the strength of that disclosed alloy has been assessed only for an alloy that is solidified by extrusion. The inventors of the present application have determined that the static strength is superior, but the dynamic strength of that disclosed alloy is not sufficient when this alloy is powder-forged at the general heating temperature of 450.degree.-550.degree. C.
A powder forging method of producing an aluminum alloy that satisfies both the static strength and the dynamic strength has not yet been achieved.